The primary objective of this mentored clinical scientist development award is to acquire the skills and expertise needed to become an independent investigator in the rheumatic diseases. This will occur through a period of intensive didactic and research training in the Division of Rheumatology at the Johns Hopkins University School of Medicine. The scientific objective of this proposal is to define the mechanisms underlying the specific immune response to histidyl-tRNA synthetase (HRS, Jo-1) in patients with autoimmune myositis and interstitial lung disease. It is known that the majority of myositis-specific autoantigens are unified by their susceptibility to cleavage by the cytotoxic lymphocyte protease granzyme B (GrB). However, the relevance of this unique property of autoantigens remains unknown. We propose that (i) the T cell response to HRS is directed at the GrB cleavage site, and (ii) that conformation and cleavability of HRS by GrB is altered in the tissue in which the autoimmune response is initiated and propagated. This proposal will address these hypotheses in Jo-1-positive patients with autoimmune myositis and interstitial lung disease, through the following specific aims: 1. To study the role of the HRS grB cleavage site in defining its immunodominant CD4+ T cell epitope. T cells from myositis patients will be probed for anti-HRS responses in-vitro using purified protein and peptides that span the GrB cleavage site. 2. To identify whether the CD8+ cytotoxic T cells in myositis patients are HRS-specific. A predictive approach will be used to identify a set of HLA-restricted HRS peptides that react with specific cytotoxic lymphocytes in myositis patients, and CD8+ T cell lines will be assessed for their ability to lyse specific target cells. 3. To determine whether an immunogenic (grB- cleavable) conformation of HRS is differentially expressed in muscle and lung tissue in patients with myositis/ILD. Lung and muscle tissue samples from patients with myositis/ILD will be probed using novel antibody reagents that recognize the GrB cleavage site. These studies will provide important information on the role of the GrB cleavage site and/or its cleavage in the immune response to HRS, as well as on tissue-specific changes in autoantigen structure that might account for its targeting in myositis/interstitial lung disease.